The known prior art includes a quantitative segmental pulse volume recorder employed as a clinical tool..sup.(1) This device is adapted to obtain hemodynamic data in terms of pulse volume amplitude, pulse contour, and limb pressure, usable in pre-operative, operative and post-operative applications to provide a measure of the functional severity of occlusive diseases, as well as an objective base line for later comparisons. The known device includes a plurality of selectively applied pneumatic cuffs which are applied to portions of the body of a patient in areas of palpable pulses. FNT (1) See: Quantitative Segmental Pulse Volume Recorder, SURGERY, St. Louis, Vol. 72, No. 6, pp. 873-887; December 1972; copyright 1972, the C. U. Moody Co.
The nature of ocular plethysmography forms no part of the present disclosure, except as insofar as to describe the operation of the disclosed embodiment. A comparable device is disclosed in U.S. Pat. No. 3,911,903, granted Oct. 14, 1975 to W. Gee et al.
The practice of ocular plethysmography implies the use of an ocular plethysmograph in order to measure the minute volume fluctuations of the ocular globe and at various levels of internal, time-average pressure within the globe. The internal pressure is changed by varying suction applied to a small eye cup of approximately 12mm diameter attached (by the suction ) directly to the sclera of the eye. An empirical correlation between the vacuum in the cup (of a peculiar, arbitrary form) and the pressure within the ocular globe has been established by Galin et al..sup.( 2),and by Gee et al.sup.( 3) independently. In the disclosed device, this correlation is incorporated into the dial of an "ocular pressure" gauge, which is actually a vacuum gauge reading negative gauge pressure in the eye cup. At low vacuums, of the order of 50mmHg, the ocular pulse may be recorded with a properly configured system that has the necessary sensitivity (of the order of 0.1mm.sup.3) to resolve fluctuations of the ocular globe. In addition, the vacuum on the ocular globe may be increased until the ocular pulse disappears from the output of the plethysmograph. The ocular pressure at which the pulse disappeared may be interpreted as the systolic pressure of the ocular pulse. The medical significance of a recording of the ocular pulse and its systolic pressure is beyond the scope of the present disclosure. FNT (2) Galin, M. A.; Bara, I.; Best, M.: The Nature of the Ocular Pulse. HEADACHE, 9: 112-118, 1969. FNT (3) Gee, W. et al: Ocular Pneumoplethysmography in Carotid Artery Disease. MED INSTRUMENTATION, 8: 244-248, 1974.